Morphology of testicular parenchyma adjacent to germ cell tumours. An interim report.

A comparative morphological analysis of parenchyma adjacent to testicular germ cell tumours (TGCT) was performed in a series of 181 orchidectomy specimens: 86 with seminomas (Se), 72 with nonseminomatous germ cell tumours (NS) and 23 with combined tumours (CT, which have a Se and a NS component). The following morphological features were semiquantitatively scored: spermatogenesis (modified Johnsen score); amount of tubular atrophy; amount of carcinoma in situ (CIS); amount of intertubular tissue. Absence and presence was scored for the following features: lymphocytic infiltrate surrounding and invading CIS; intratubular seminoma (ISe); intratubular nonseminoma (INS); microlithiasis; diffuse and nodular hyperplasia of Leydig cells; angioinvasiveness; testicular angiopathy. Using non-parametric statistics these features were correlated with each other and with tumour type, tumour size and age of the patient. Se-patients presented at significantly higher age than NS-patients (36 vs 29 years, p=0.001). The age of patients with CT (32 years) was in between that of Se- and NS-patients. No correlation was found between patient age and tumour size. Parenchyma adjacent to Se, compared to parenchyma adjacent to NS had the following significant differences: a lower Johnsen score (5.6 vs 7.2, p=0.005); less frequent (85% vs 97% of specimens, p=0.016) and a lesser amount of CIS (26% vs 32% of tubules, p=0.015); more frequent peri- (80% vs 60% of specimens, p=0.001) and intratubular (68% vs 30% of specimens, p=0.001) lymphocytic infiltrates; more extensive tubular atrophy (36% vs 15% of tubules, p=0.001); and a larger area of intertubular tissue (42% vs 34% of parenchyma area, p=0.016). The pooled Se and CT had a significantly higher frequency of ISe than the NS (31% vs 17% of specimens, p=0.036). With one exception INS was only found adjacent to NS or CT, with a frequency of 16%, and 20% of the specimens, respectively. It was significantly associated with angio-invasiveness. In specimens lacking angio-invasion the frequency of INS was 6%. The correlation of INS with tumour size and patient age was studied in a series of 145 NS and CT (95 from the original series supplemented by 50 newer cases). In this series INS was significantly associated with smaller tumours and younger patients. Extensive tubular atrophy was significantly correlated with higher age, the diagnosis of Se, a low Johnsen score, and the presence of angiopathy. The more tubular atrophy, the less CIS (both in incidence and amount). Inversely, a higher Johnsen score is associated with smaller tumours, the diagnosis of NS or CT, a higher incidence and a larger amount of CIS, and little tubular atrophy. Tubules with mature spermatogenesis were found in 42% of the specimens regardless of tumour type. We conclude that ISe and INS are probably frequent intermediate stages between CIS and Se and NS, respectively. The features of parenchyma adjacent to Se are probably due to the host response elicited by the invasive Se, which secondarily also affects CIS. The long time to clinical presentation allows the host to eradicate most of the CIS by the time the tumour is surgically removed. The much less extensive morphological features of a host response in parenchyma adjacent to NS support the contention that NS originates as INS, behind the blood/testis barrier, without exposure of the host to tumour cells with a seminomatous phenotype (CIS- or Se cells). Microlithiasis and testicular angiopathy are frequent, but not specific findings in parenchyma next to TGCT. Their relationship with the development with TGCT is unexplained.

Essential role for protein kinase B (PKB) in insulin-induced glycogen synthase kinase 3 inactivation. Characterization of dominant-negative mutant of PKB.

Activation of phosphatidylinositide 3'-OH kinase (PI 3-kinase) is implicated in mediating a variety of growth factor-induced responses, among which are the inactivation of glycogen synthase kinase-3 (GSK-3) and the activation of the serine/threonine protein kinase B (PKB). GSK-3 inactivation occurs through phosphorylation of Ser-9, and several kinases, such as protein kinase C, mitogen-activated protein kinase-activated protein kinase-1 (p90(Rsk)), p70(S6kinase), and also PKB have been shown to phosphorylate this site in vitro. In the light of the many candidates to mediate insulin-induced GSK-3 inactivation we have investigated the role of PKB by constructing a PKB mutant that exhibits dominant-negative function (inhibition of growth factor-induced activation of PKB at expression levels similar to wild-type PKB), as currently no such mutant has been reported. We observed that the PKB mutant (PKB-CAAX) acts as an efficient inhibitor of PKB activation and also of insulin-induced GSK-3 regulation. Furthermore, it is shown that PKB and GSK-3 co-immunoprecipitate, indicating a direct interaction between GSK-3 and PKB. An additional functional consequence of this interaction is implicated by the observation that the oncogenic form of PKB, gagPKB induces a cellular relocalization of GSK-3 from the cytosolic to the membrane fraction. Our results demonstrate that PKB activation is both necessary and sufficient for insulin-induced GSK-3 inactivation and establish a linear pathway from insulin receptor to GSK-3. Regulation of GSK-3 by PKB is likely through direct interaction, as both proteins co-immunoprecipitate. This interaction also resulted in a translocation of GSK-3 to the membrane in cells expressing transforming gagPKB.

Epidermal growth factor induces phosphorylation of extracellular signal-regulated kinase 2 via multiple pathways.

Expression of p21rasAsn-17, a dominant negative mutant of p21ras that blocks p21ras activation by growth factors, inhibits activation of extracellular signal-regulated kinase 2 (ERK2) by insulin and platelet-derived growth factor in rat-1 cells [A. M. M. de Vries-Smits, B. M. T. Burgering, S. J. Leevers, C. J. Marshall, and J. L. Bos, Nature (London) 357:602-604, 1992]. Here we report that expression of p21rasAsn-17 does not abolish epidermal growth factor (EGF)-induced phosphorylation of ERK2 in fibroblasts. Since EGF activates p21ras in these cells, this indicates that EGF induces a p21ras-independent pathway for the phosphorylation of ERK2 as well. We investigated whether activation of protein kinase C (PKC) or increase in intracellular calcium could be involved in p21ras-independent signaling. In rat-1 cells, inhibition of either PKC, by prolonged 12-O-tetradecanoylphorbol-13-acetate (TPA) pretreatment, or calcium influx, by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) pretreatment, did not abolish EGF-induced ERK2 phosphorylation. However, a combined inhibition of both p21ras and calcium influx, but not PKC, resulted in a complete inhibition of EGF-induced ERK2 phosphorylation. In contrast, in Swiss 3T3 cells, inhibition of both p21ras activation and TPA-sensitive PKC, but not calcium influx, inhibited EGF-induced ERK2 phosphorylation. These results demonstrate that in fibroblasts, EGF induces alternative pathways of ERK2 phosphorylation in a cell-type-specific manner.

cAMP antagonizes p21ras-directed activation of extracellular signal-regulated kinase 2 and phosphorylation of mSos nucleotide exchange factor.

In fibroblasts, stimulation of receptor tyrosine kinases results in the activation of the extracellular signal-regulated kinase 2 (ERK2). The major signalling pathway employed by these receptors involves the activation of p21ras and raf-1 kinase. Here we show that in NIH3T3 and rat-1 fibroblasts, elevation of the intracellular cAMP level results in the inhibition of ERK2 activation induced by PDGF, EGF and insulin treatment. Analysis of various signalling intermediates shows that cAMP interferes at a site downstream of p21ras, but upstream of raf-1 kinase. Inhibition by cAMP depends on both the cAMP concentration and the absolute amount of p21ras molecules bound to GTP, suggesting a mechanism of competitive inhibition. Also TPA-induced, p21ras-independent, activation of raf-1 kinase and ERK2 is inhibited by cAMP. We have used the inhibitory effect of cAMP to investigate whether phosphorylation of mSos, a p21ras nucleotide exchange factor, is dependent on the activity of the raf-1 kinase/ERK2 pathway. We found that phosphorylation of mSos, as monitored by a mobility shift, is delayed with respect to p21ras and ERK2 activation and is inhibited by cAMP in a similar cell type- and concentration-dependent manner as the inactivation of ERK2. These results provide evidence for a model of p21ras-directed signalling towards ERK2 that feeds back on mSos by regulating its phosphorylation status and that can be negatively modulated by protein kinase A and positively modulated by protein kinase C action.